I may already know the answer to this, but I figured I'd ask here anyway. I have a non-EFI nVidia GTX 750 Ti that has been working beautifully in my Mac Pro 3,1 with the nVidia web driver on El Capitan. I decided to go on one of my "computer adventures" last night and install Windows on one of my other hard drives. I tried to boot from USB to install Windows, which didn't work (and I knew better, but tried it anyway). I was stuck with the "no boot device screen". I thought, "resetting the NVRAM should fix this." Well, it also "fixed" my computer's ability to use its graphics card - apparently the NVRAM reset sets MacOS back to its default video driver. Thus, now my card displays nothing whatsoever. I have ordered an old mac-specific card from ebay, but in the mean-time, is there a way I can get MacOS to use my card? I really would like to use my computer.